ISO 21904-2:2020 pdf download.Health and safety in welding and allied processes – Equipment for capture and separation of welding fume ‑ Part 2: Requirements for testing and marking of separation efficiency (ISO 21904-2:2020)
4 Principle
The method is based on the methods specified in EN 1093‑6 [10] and EN 1093‑7 [11] . Under test, the welding fume separation equipment is charged by welding fume generated by a welding process. The welding fume concentrations are measured in the incoming and exhausted air of the separation unit. The welding fume separation equipment under test is operated under defined conditions, according to its intended use. The emission rate of the welding fume source is measured separately.
Therefore, the welding fume generated by the source is sampled on preweighed filters over a period of time. The air volume flow rate of the welding fume separation equipment and the testing time shall be measured during the separation efficiency test. Emission rate, testing time and air volume flow rate are used subsequently to calculate the concentration of welding fume in the incoming air. Welding parameters should be the same when emission rate and separation efficiency test are performed. Before separation efficiency measurements are made, all welding fume separation equipment are charged for a period of 30 min using the welding fume source.
For equipment with filters that are not intended to be cleaned, the concentration of welding fume passing through the separation equipment is measured subsequently for a period of 30 min and the measured concentration is used, together with the welding fume concentration calculated from the welding fume emission rate, to determine the separation efficiency. For equipment with cleanable filters, an additional separation efficiency measurement is performed after a further welding period without measurement and filter cleaning.
The average of the two separation efficiencies is calculated. Two tests are performed and the average, the 95 % one-sided confidence interval and the lower confidence limit value of the separation efficiency are calculated according to ISO 2602. If the resulting lower confidence limit value is less than the required separation efficiency, consideration shall be given to improve the filter unit design.
5 Apparatus
5.1 Welding fume source, capable of maintaining an emission rate of 10 mg/s ± 2 mg/s throughout the test period.
The welding fume source shall be fitted with an extraction hood that retains all the welding fume emitted and shall be designed in such a way that it can be connected to the inlet duct of the test cabin, as described in Figure 1, or directly to welding fume separation equipment with a ducted outlet, as described in Figure 2. It shall be possible to determine the welding fume emission rate in situ without disturbing the welding set-up in any way. An example of a suitable welding fume source and parameters required to achieve the required welding fume emission rate are described in Annex B.
5.2 Test cabin, consisting of an enclosure for the welding fume separation equipment under test,connected to the welding fume source via an upstream measurement duct.
The cabin is connected to a downstream measurement duct and an air mover (see Figure 1). The air volume flow rate through the air mover is adjusted to between 95 % and 100 % of the air volume flow rate in the upstream duct, thus ensuring a small positive air pressure in the cabin.
5.3 Test arrangement for welding fume separation equipment with a ducted outlet, consisting of a welding fume source connected to the equipment via an upstream measurement duct.
The outlet of the welding fume separation equipment is directly linked to the downstream measurement duct (see Figure 2).
5.4 Air volume flow rate measurement equipment, capable of measuring rates up to 2 000 m 3 /h continuously, to within an accuracy of ±10 % or better.
The following combination of equipment is suitable.
A flow meter with a calibrated relationship between pressure difference and air volume flow rate, e.g.an orifice plate, together with a digital manometer to measure the pressure difference across it. The digital manometer shall have a logging capability or be connected to a logging system with a logging frequency of 1 min or less.
A device for measuring air volume flow rate with equivalent performance is also suitable.ISO 21904-2 pdf download.ISO 21904-2 pdf download
